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BAU02 - Discovery of new highly excited OH sources in regions of high-mass star formation

Short title: Baudry & Desmurs (2002)
Authors: Baudry, A.Desmurs, J. F.
Journal: Astronomy and Astrophysics, v.394, p.107-113 (2002)
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Target type: High_mass_SFR,EGO,UCHII
Observations category: SF.general
Facility type: single-dish
Transitions: OH_1612,OH_1665,OH_1667,OH_1720,OH_13441,OH_13435

Abstract
We have carried out sensitive observations of the highly excited <SUP>2</SUP>Pi<SUB>3/2</SUB>, J=7/2 state of OH (290 K above the ground-level) at 13,441 MHz (F=4-4) and 13,435 MHz (F = 3-3) in both right and left circular polarizations with the Effelsberg 100-m telescope. Our sample included 27 compact or ultra-compact HII regions. Most of them have been selected from our previous J=5/2 OH maser survey of star-forming regions taken from the IRAS point-source catalog. We have observed weak <SUP>2</SUP>Pi<SUB>3/2</SUB>, J=7/2, F = 4-4 and 3-3 absorption in 7 sources and discovered 3 new weak F = 4-4 maser sources at 13,441 MHz in addition to W3(OH). The new sources, 20081+3122 (ON1), 21413+5442 and G11.90-0.14, are 50 to 100 times or more weaker than the 13,441 MHz peak flux density observed in W3(OH). 21413+5442 and G11.90-0.14 exhibit extremely narrow velocity extents of the order of 0.4 km s<SUP>-1</SUP>. However, in ON1 there are two groups of narrow velocity features separated by about 14 km s<SUP>-1</SUP>; these two groups are also observed in lower rotational levels and suggest complex kinematics in the envelope of the young ultra-compact HII region. Apart from a very weak, polarized, and narrow J=7/2, F = 3-3 emission feature lying on the red wing of the 13,435 MHz absorption feature in W3(OH) no J=7/2, F =3-3 emission was discovered. We conclude that the 13,441 MHz OH maser emission from W3(OH) remains exceptionally strong but not unique. In contrast with the J=5/2, 6035 MHz maser emission observed in a large number of star-forming regions, J=7/2, 13,441 MHz emission is not widespread. This is expected from OH maser theory, and because the involved J=7/2 levels are high in the OH energy ladder and not directly connected to the ground-state.

Abstract

We have carried out sensitive observations of the highly excited 2Pi3/2, J=7/2 state of OH (290 K above the ground-level) at 13,441 MHz (F=4-4) and 13,435 MHz (F = 3-3) in both right and left circular polarizations with the Effelsberg 100-m telescope. Our sample included 27 compact or ultra-compact HII regions. Most of them have been selected from our previous J=5/2 OH maser survey of star-forming regions taken from the IRAS point-source catalog. We have observed weak 2Pi3/2, J=7/2, F = 4-4 and 3-3 absorption in 7 sources and discovered 3 new weak F = 4-4 maser sources at 13,441 MHz in addition to W3(OH). The new sources, 20081+3122 (ON1), 21413+5442 and G11.90-0.14, are 50 to 100 times or more weaker than the 13,441 MHz peak flux density observed in W3(OH). 21413+5442 and G11.90-0.14 exhibit extremely narrow velocity extents of the order of 0.4 km s-1. However, in ON1 there are two groups of narrow velocity features separated by about 14 km s-1; these two groups are also observed in lower rotational levels and suggest complex kinematics in the envelope of the young ultra-compact HII region. Apart from a very weak, polarized, and narrow J=7/2, F = 3-3 emission feature lying on the red wing of the 13,435 MHz absorption feature in W3(OH) no J=7/2, F =3-3 emission was discovered. We conclude that the 13,441 MHz OH maser emission from W3(OH) remains exceptionally strong but not unique. In contrast with the J=5/2, 6035 MHz maser emission observed in a large number of star-forming regions, J=7/2, 13,441 MHz emission is not widespread. This is expected from OH maser theory, and because the involved J=7/2 levels are high in the OH energy ladder and not directly connected to the ground-state.

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Detection table from Baudry & Desmurs (2002)

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ID	Obs. RA	Obs. Dec	l	b	Group id	Source name	Image	Line	Frequency	Polarization	V_peak	FWHM	F_peak	Telescope	RMS	Beam	Detection	Class	Dist. (parallax)	Date
	(J2000)	(J2000)	(deg.)	(deg.)				OH	(MHz)		(km/s)	(km/s)	(Jy)		(Jy)	(arcsec)	Yes/No		(kpc)
1	02 27 3.9	+61 52 24.6	133.9474	1.0642	G133.947+1.064	W3(OH)	Image	13441 MHz;	13441	RCP	-43.91	0.39	0.72	EFF	0.110	60	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		5;6;10 May 1999
	02 27 3.9	+61 52 24.6	133.9474	1.0642	G133.947+1.064	W3(OH)	Image	13441 MHz;	13441	RCP	-43.03	0.37	19.7	EFF	0.110	60	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		5;6;10 May 1999
	02 27 3.9	+61 52 24.6	133.9474	1.0642	G133.947+1.064	W3(OH)	Image	13441 MHz;	13441	RCP	-42.37	0.35	7.72	EFF	0.110	60	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		5;6;10 May 1999
	02 27 3.9	+61 52 24.6	133.9474	1.0642	G133.947+1.064	W3(OH)	Image	13441 MHz;	13441	LCP	-44.01	0.47	0.83	EFF	0.110	60	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		5;6;10 May 1999
	02 27 3.9	+61 52 24.6	133.9474	1.0642	G133.947+1.064	W3(OH)	Image	13441 MHz;	13441	LCP	-43.11	0.3	25.6	EFF	0.110	60	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		5;6;10 May 1999
	02 27 3.9	+61 52 24.6	133.9474	1.0642	G133.947+1.064	W3(OH)	Image	13441 MHz;	13441	LCP	-42.49	0.31	10.2	EFF	0.110	60	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		5;6;10 May 1999
7	18 12 11.6	-18 41 29.6	11.9041	-0.1416	G11.904-0.141	G11.90-0.14	Image	13441 MHz;	13441	RCP	43.09	0.23	0.21	EFF	0.020	60	+H₂O -CH₃OH I +CH₃OH II +OH	SFR		5;6;10 May 1999
8	21 43 1.4	+54 56 16.3	98.0354	1.4458	G98.035+1.446	21413+5442	Image	13441 MHz;	13441	RCP	-61.47	0.16	0.39	EFF	0.020	60	+H₂O +CH₃OH I +CH₃OH II +OH	SFR_MIXED		5;6;10 May 1999
	21 43 1.4	+54 56 16.3	98.0354	1.4458	G98.035+1.446	21413+5442	Image	13441 MHz;	13441	LCP	-61.47	0.17	0.38	EFF	0.020	60	+H₂O +CH₃OH I +CH₃OH II +OH	SFR_MIXED		5;6;10 May 1999
10	20 10 9.1	+31 31 34.4	69.5399	-0.9760	G69.540-0.976	20081+3122	Image	13441 MHz;	13441	RCP	-0.13	0.23	0.48	EFF	0.020	60	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		5;6;10 May 1999
	20 10 9.1	+31 31 34.4	69.5399	-0.9760	G69.540-0.976	20081+3122	Image	13441 MHz;	13441	RCP	14.01	0.15	0.09	EFF	0.020	60	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		5;6;10 May 1999
	20 10 9.1	+31 31 34.4	69.5399	-0.9760	G69.540-0.976	20081+3122	Image	13441 MHz;	13441	LCP	-0.13	0.22	0.47	EFF	0.020	60	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		5;6;10 May 1999
	20 10 9.1	+31 31 34.4	69.5399	-0.9760	G69.540-0.976	20081+3122	Image	13441 MHz;	13441	LCP	14.02	0.19	0.08	EFF	0.020	60	+H₂O +CH₃OH I +CH₃OH II +OH	SFR		5;6;10 May 1999

Non-detection table from Baudry & Desmurs (2002)